Hmmmmm, suggestions....I don't have any children so I don't really know...
Do what is best for your kids. However, understand, that unless her OM has some type of prior charge of inappropriate behavior with a child---she can legally introduce to whomever she wants. Sucks---but check with your state or local laws.
It is hard to stand and I can relate to going back and forth.
Hang in there...
Valentine
Aug '06: H moved out July '08: H had a kid with the OW May 12 '09: emancipation day
"Life moves pretty fast. You don't stop and look around once in a while, you could miss it." -Ferris Bueller